memorial brass:
an engraved metal plate used as a commemorative monument.
Sometimes these were set vertically, usually in a wall, but usually
they were set horizonatlly, flush with the pavement of
a church, to mark a tomb.
The engraved areas were often filled with pigment.

mosaic:
A decoration created by setting small pieces of glass, stone, or marble in
a matrix- often concrete. Wall mosaics were most prevelent in the Early
Christian and Byzantine periods, during which they were a very important
form of wall decoration.